Don't Dwell on Mistakes, Look Beyond and Move Forward;
Accept that it happened and can't be changed.
Know there is always something to learn from it.
Look to understand it and the factors that caused it.
How could you have recognized the mistake earlier?
How can you avoid the mistake next time?
Are there similar things that might have a related mistake to avoid?
What has changed now to ensure that mistake doesn't reoccur?
Who else should know about this and learn from it?
So, once you have done this initial analysis of the mistake, its time to move on. No matter how big the mistake was, just let it go and move on.